Rear projection displays or televisions include an image-generating system positioned behind a display screen, opposite from where viewers watch the images that are projected onto the screen. Typical rear projection televisions employ three scanning projection cathode-ray tubes (CRTs), one for each of the primary color components red, green, and blue.
Projection cathode-ray tubes are cumbersome, as are the optical systems for projecting and superimposing the separate color component images on the display screen. As a result, early rear projection televisions required large, floor-mounted cabinets to accommodate the cumbersome projection CRTs and their optical systems. The cabinets include pedestals, or pedestal portions, that are positioned below the display screen and contain the projection CRTs and the optical systems.
Some rear projection displays have employed a single large transmissive pixelated liquid crystal display (LCD) panel with optics analogous to those of a front projection display. These rear projection displays were bulky and heavy and directed to specialized display applications such as trade show displays. Examples of rear projection displays were available from Barco NV of Kortrijk, Belgium and Optoma Corp. of Taipei, Taiwan.
The miniaturization of liquid crystal displays has allowed rear projection televisions to be reduced in size while maintaining or enlarging display screen size. Likewise, other miniaturized electronic imaging devices, such as pixelated reflective imaging elements referred to as digital micromirror devices and available from Texas Instruments, Incorporated, have also allowed rear projection televisions to be reduced in size while maintaining or enlarging display screen size.
As one example, a rear projection television incorporates three small-size LCDs (e.g., 1.3 inch or 3.3 cm, diagonal) for separately controlling the three primary color components red, green and blue. Such a rear projection television is available from Sony Corporation as the Grand Wega™ model (model number KF-50XBR800). As another example, a rear projection television employing a digital micromirror device (e.g., 0.8 inch, 2.0 cm, diagonal) is the Model HLM507W projection television available from Samsung Corporation. Both of these rear projection television include display screens with 50-inch (127 cm) diagonal measurements.
Rear projection televisions with miniaturized electronic imaging devices (e.g., LCDs or digital micromirror devices) have been sized and have pedestals to accommodate table-top viewing. For example, the Grand Wega™ model available from Sony Corporation has a pedestal with a height of 12 inches (30.5 cm) and a depth of 14 inches (35.5 cm). Similarly, the Model HLM507W available from Samsung Corporation has a pedestal with a height of 8 inches (20 cm) and a depth of 17 inches (43 cm). With the 16:9 aspect ratios of the display screens, the pedestal of the Grand Wega™ has a height and depth that are respectively about 0.57 and 0.51 the height of the display screen, and the Model HLM507W has a height and depth that are respectively about 0.31 and 0.67 the height of the display screen. As referenced herein, therefore, table-top rear projection televisions include a cabinet pedestal having a height and a depth that are each less than or equal to about 0.65 the height of the display screen.
Available table-top rear projection televisions based upon miniaturized imaging elements, such as LCDs or digital micromirror devices, are expensive. Multiple miniaturized LCDs, and their triplicate optical systems, increase the cost and complexity of the televisions. Digital micromirror devices are based upon an expensive and complex proprietary technology. In addition, miniaturized imaging elements require powerful optical elements to magnify or project the video images. The optical elements must magnify an image from each LCD (e.g., 1.3 inch or 3.3 cm, diagonal) or a digital micromirror device (e.g., 0.8 inch, 2.0 cm) to the full extent of a 50-inch (127 cm) display within the confines of a table-top cabinet. In addition to being powerful, such optical elements are subject to distortion. Providing such powerful optical elements with acceptable distortion properties further adds to the expense of these televisions.
Accordingly, the present invention provides a table-top rear projection television that employs a single large-panel (e.g., 7 inch-15 inch or more, 17.5 cm-38 cm, diagonal), multi-color transmissive imaging device (e.g., an amorphous silicon liquid crystal display). The rear projection television has a cabinet with a pedestal having a height and a depth that are each less than or equal to about 0.65 the height of the display screen, with the factor being less than about 0.55 in some embodiments. The display screen may have any aspect ratio of a wide format (e.g., 16:9, 15:9, 16:10) or a conventional format (i.e. 4:3).
An illumination system is positioned in the pedestal and directs light along an optical path. The large-panel LCD receives the light and imparts video images on the light. A short conjugate fold mirror and a short vertex-to-vertex projection lens successively receive the light with the imparted video images, and a long conjugate fold mirror then folds the optical path from the projection lens and directs the light through the display screen.
The rear projection television of the present invention, and the associated optical elements, reverse the course of conventional design development for rear projection televisions by employing a large-panel LCD in a table-top television. The use of the large-panel LCD relaxes the performance requirements of the projection optics and can provide rear projection televisions at significantly reduced costs.
Additional description and implementations of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.